The present invention relates to apparatus and methods for determining the susceptibility of certain liquids to coagulate and subsequently to lyse. The apparatus and methods of the present invention are particularly suitable for assessing blood coagulation status in a patient. These may also be adapted to assess fibrinolytic status in a patient.
A wide variety of laboratory clotting tests are based on the phenomenon of measuring as an endpoint, a change of phase when a test solution changes from a liquid to a coagulated form. This change is due to the conversion of a soluble plasma protein fibrinogen to an insoluble one, fibrin by the action of the enzyme thrombin. The reverse change is also made use of in tests where one is measuring the lyric activity of a solution, whereby insoluble fibrin is broken down to soluble degradation products by the enzyme plasmin.
For example, blood clotting tests are important to assess likelihood of bleeding in patients treated with anticoagulants or with haemostatic defects. The endpoint of the most frequently performed clotting test, the skin bleeding time, is the cessation of blood flow from a standardised skin incision. This is usually determined by the periodic blotting of the wound site until blood flow from the wound ceases. This test is particularly prolonged by platelet defects. Other clotting tests are usually carried out by mixing test plasmas with specific reagents and timing to an endpoint when the mixture suddenly clots. The clotting endpoint is usually determined physically, as in a tilt-tube, or optically by increased turbidity, as in a photoelectric clotting machine.
This current innovation has been stimulated by a number of precursore developments. The first of these is the use of convenient dry cards such as the Nyco Card (Nyco Med Pharma) for rapidly testing antibody reactions (e.g. FDP, D-dimer). These devices comprise porous modules which are faced with an immunoreactive membrane. Test samples are applied to such surfaces and are drawn through by capillary action. Antigens or antibodies for test are quantitated by a color reaction after sequential washing and incubation steps. Secondly, small capillary coagulation testing devices have also recently been developed. These are based on blood or plasma drawn into a small capillary with coagulation detected using either a laser (Bio Track, Ciba-Corning) or pressure sensing systems (Nyco Med). One such device features dry coagulation reagents while the other relies on uncoated glass capillaries.
Unfortunately, these prior art devices are quite complex requiring laser or pressure sensing equipment.
It will be clear to persons skilled in the art that there is a need for simpler, more convenient and adaptable methods and apparatus for measuring the susceptability of liquids to coagulate or lyse over currently existing methods and apparatus. It is desirable to provide small testing modules which may be used at the bedside in a portable form or alternatively can be assembled together to process much larger numbers of samples in a central laboratory.
Currently there is a significant market for rapid portable methods in the coagulation/lysis testing area. Larger laboratories usually purchase expensive sophisticated equipment for massive scale operation. Small inexpensive bedside testing units have an important role in a number of clinical situations especially where prompt interpretation of patient results is required and when screening tests are only rarely positive.